Warping in a Large Laminated-MDF Door

Waterbased glue caused this MDF layup to warp in service. March 4, 2009

I'm building MDF doors. The face is an MDF ranger board 2' by 8' by 3/4 and there are 8'' by 15" holes done by a CNC evenly spaced. I laminated the face to another 2' by 8' by 1/2" MDF. I used yellow glue and I clamped them flat overnight. When I pulled out the clamps they where bowed and cupped (concave to the face) and the next day it was even worse. What should I do not to run into this problem and is there any way to make them flat again?

Forum Responses
(Laminate and Solid Surfacing Forum)
From contributor L:
Use a non water base glue.

From the original questioner:
These are the door that cupped and bowed.

From the original questioner:
Here you can see the bow – it’s 1" at the center of the door height.

From contributor R:
You could try a cleat on edge screwed to the back. Tall doors usually need it anyway. The water based glue was the problem.

From contributor J:
Hafelle makes a 'straightener' for bowed doors like that. If you don't have the catalog it's available in PDF format on their website.

From contributor A:
We have always found doors we made in a similar way to be unpredictable; sometimes warping like that a week or two later. We now do everything in a frame and panel construction with loose tongues. You can still glue in a moulding if you use 22mm or 25mm MDF for the frames. Hettich makes concealed hinges that cope with the extra thickness and the doors stay completely flat. We found that not having to clean the rounded corners out by hand compensated to a degree the extra time involved. We don't have access to a CNC.